1. Field of the Invention
This invention relates to the measurement of the polarization of a “hyperpolarized resonant” substance: that is, a substance whose nuclear or electronic spins are not in thermal equilibrium (i.e. hyperpolarized) and which exhibit magnetic resonance.
2. Prior Art
Hyperpolarized noble gases have been shown to be very effective for magnetic resonance imaging of the lungs, and their use in clinical diagnosis is poised as a new procedure. For this reason, an instrument to measure the polarization of the gas is needed for the production, distribution and use of these gases. There are two methods for this in use today.
In one method, (the “small angle tip” method) the polarization vector is tipped away from the defined direction of polarization (i.e. the ambient magnetic field) by a small angle θ, say 5°. The polarization then precesses about the field, and the transverse component of magnetization induces a voltage in a suitably placed coil. This magnitude of this voltage (known as the “free induction decay”) is proportional to the polarization. After the decay of the transverse polarization, the remaining polarization is reduced by a factor (1−cos θ). Thus, some polarization is lost with each measurement. This method requires what is essentially a (suitably modified) magnetic resonance, or magnetic resonance imaging instrument.
In another method, a coil is wound round the tube which conveys hyperpolarized gas to a patient. When the composition of the gas passing along this tube changes from air to hyperpolarized gas, a voltage is induced in this coil. This voltage is integrated, and the result is proportional to the polarization. The disadvantage of this method is that it can be used only once, at the instant of administration to a patient.